1. Field of the Invention
The present invention relates to steering assist systems, and more particularly, to a steering assist system that controls steering so that a subject vehicle can follow a preceding vehicle.
2. Description of the Related Art
In recent years, steering assist systems have been developed. In steering assist systems, a preceding traveling ahead of a subject vehicle is detected by analyzing an image taken by an image taking means, such as a stereo camera, or analyzing reflected waves of radio waves emitted from a radar apparatus, and the steering angle and so on of the subject vehicle are automatically controlled so that the subject vehicle can follow the preceding vehicle (for example, see Japanese Unexamined Patent Application Publication No. 2006-298008).
In a steering assist system disclosed in Japanese Unexamined Patent Application Publication No. 2007-261449, when there is no preceding vehicle, the steering angle and so on of a subject vehicle are automatically controlled on the basis of information about traffic lines detected on the right and left sides of the subject vehicle so that the subject vehicle will not deviate from the traffic lines. Another type of steering assist system has been developed in which the aim of steering assist is switched from preceding vehicle follow-up to traffic line follow-up when a preceding vehicle travels far from a subject vehicle (for example, see Japanese Unexamined Patent Application Publication No. 2005-332192).
In the present invention, continuous lines and broken lines marked on the road surface, for example, a road center line such as a no-passing line, and a separating line for separating a side strip and a roadway, are referred to as traffic lines, and a region defined by two traffic lines on the road is referred to as a traveling lane.
In a case in which the preceding vehicle is traveling close to or over the right or left traffic line, when steering assist is continued so that the subject vehicle follows the preceding vehicle, the subject vehicle is also going to travel close to or over the right or left traffic line. This gives the driver a feeling of insecurity.
However, for example, when the aim of steering assist is switched from preceding-vehicle follow-up to traffic-line follow-up in order to avoid the above-described problem, since a traveling target point, that is, a point defined in real space so as to determine the traveling route of the subject vehicle is set in the center of the traveling lane of the subject vehicle in normal traffic-line follow-up control, the traveling target point is rapidly switched from the preceding vehicle near the traffic line to the center of the traveling lane.
For this reason, the subject vehicle that has been traveling close to the right or left traffic line rapidly turns its traveling direction toward the center of the traveling lane. Therefore, the driver feels as if the subject vehicle was pulled back toward the center of the traveling lane. This gives the driver a feeling of discomfort.